Electromagnetic force motor with internal eddy current damping

Abstract

The invention is directed to an improved electromagnetic force motor (10) with internal eddy current damping. In the preferred embodiment, the motor is comprised of a body (11), a pair of permanent magnets (15 L , 15 R ), an electromagnetic coil (20), and an armature (13). The armature is positioned with respect to the body so as to define two variable-reluctance working air gaps (30, 31) and a constant-reluctance non-working air gap (29). The permanent magnets face one another and are mounted on the body. The body and armature are both adapted to conduct magnetic flux. Each working air gap contains a magnetic flux that is the algebraic sum of a flux attributable to the permanent magnets and a flux attributable to the coil. The non-working air gap contains flux attributable only to the permanent magnets. A current-conducting member (14) is attached to the armature and positioned within the non-working air gap. The current-conducting member moves linearly in the non-working air gap in a direction substantially perpendicular to the flux therein such that eddy currents are induced in the member. The elements of the motor are configured such that the eddy currents are a function of the velocity of the armature relative to the body, but are not a function of changes in the flux either attributable to the coil or attributable to the position of the armature. The eddy currents provide damping of armature velocity, and result in an electromagnetic force motor with improved dynamic performance and greater stability.

What is claimed is: 
     
       1. In a motor having an armature mounted for limited displacement relative to a body, having a high reluctance permanent magnet, and having an electromagnetic coil, said body and armature being adapted to conduct magnetic flux, said armature defining with said body a plurality of variable-reluctance working air gaps and at least one constant-reluctance non-working air gap, each of said working air gaps containing a net flux that is the algebraic sum of a flux attributable to said magnet and a flux attributable to said coil, said non-working air gap containing only flux attributable to said magnet, the improvement which comprises: a current-conducting member attached to said armature and arranged to move in said non-working air gap in a direction having a component substantially perpendicular to the flux therein such that eddy currents will be induced in said member to damp the velocity of said armature;   the elements of said motor being so configured and arranged that said eddy currents are a function of the velocity of said armature relative to said body, but are not a function of changes in the flux attributable to said coil or attributable to the position of said armature relative to said body.   
     
     
       2. The improvement as set forth in claim 1 wherein said armature moves linearly relative to said body. 
     
     
       3. In a motor having an armature mounted for limited displacement relative to a body, having a high reluctance permanent magnet, and having an electromagnetic coil, said body and armature being adapted to conduct magnetic flux and operatively arranged to produce variable magnetic forces on said armature as a function of the current in said coil, the improvement which comprises: a current-conducting member mounted on said armature so as to move through magnetic flux attributable to said magnet to produce eddy current damping of the velocity of said armature;   the elements of said motor being so configured and arranged that magnetic flux attributable to changes in the current in said coil or attributable to changes in the position of said armature relative to said body does not pass through said conducting member.   
     
     
       4. The improvement as set forth in claim 1 wherein said motor includes a first portion adapted to conduct flux attributable to said coil through said working air gaps and said armature, and includes a second portion that contains said permanent magnet and said non-working air gap, and wherein said armature is arranged in said first and second portions. 
     
     
       5. The improvement as set forth in claim 4 wherein said first and second portions are cylindrical and concentric, and wherein said working air gaps and said armature are arranged in said first and second portions, and wherein said current-conducting member is arranged within said second portion.